Holley/Demon Carb stumble

[PRH]

The 8 psi was 1 minute and 55 seconds

Edit: per A Gal
I would have to raise the regulator pressure to get a acurite reading. reg is dumping fuel because it's getting close to the regulated 9 psi

I would try that...... raise the pressure to 11 or 12 and then do the test at 9psi.

If you want to run 9psi system pressure, it needs to maintain that pressure while pumping a gallon in under 85 seconds.

 

[PRH]

The system pressure should set to a number 1/2 to 1 psi lower than what the system can maintain for your power level(unless it will maintain more than enough pressure, then set it to where you want).

You’re not understanding what I’m saying.
Let’s say you turn up the regulator to 15psi, and retest with the valve to set to maintain 9psi, and it still takes 115 seconds to pump a gallon.

Then, in operation ....... you set the pressure to 9psi....... and the pressure drops as soon as the motor starts making over about 375hp...... and the floats drop.

 

[Cudafever]

That's the other thing, this test was done with only one line (the primary bowl line) removed. the secondary was still hooked up to the carb. If i go to 11 psi i will have to remove the sconday fuel feed line and add it to my test(would need a Y fitting) or plug it off

You’re not understanding what I’m saying.
Let’s say you turn up the regulator to 15psi, and retest with the valve to set to maintain 9psi, and it still takes 115 seconds to pump a gallon.

Then, in operation ....... you set the pressure to 9psi....... and the pressure drops as soon as the motor starts making over about 375hp...... and the floats drop.

I disagree!!!
The regulator is Pinching off the Flow as it is getting up to the regulated PSI so more of the fuel that the pump is pushing is being return to the fuel tank. AT 9 PSI there is (0) flow out of the hose and there can't be or the pressure would continue to creep up above 9 psi.
But I'm willing to retest. 12 Psi at the req, dropping it to 9 psi with the ball valve and a container.
Stay tune

 

[Cudafever]

Ok no retest.
I don't have a cap to plug the secondary feed to the carb and i don't have a Y to tie them both together. and i'm not pushing 12 psi to my needle and seat. IF it was a rubber hose i would be way tempted to pinch of the secondary line with vice grips, but it is a braided hose.
I get this..VVVVVVVVVVVVVVVV

You’re not understanding what I’m saying.
Let’s say you turn up the regulator to 15psi, and retest with the valve to set to maintain 9psi, and it still takes 115 seconds to pump a gallon.

Then, in operation ....... you set the pressure to 9psi....... and the pressure drops as soon as the motor starts making over about 375hp...... and the floats drop.

But if i have enough "fuel flow" to support close to 600 HP at 6 PSI.(One gal in 53 seconds) Do you really think i'm losing that much more flow at 9 PSI?

"For a 500hp motor it should take less than 85 seconds."
550hp - 78 seconds
600hp - 72 seconds

 

[fishmens67]

Are you using 1/2 " fuel line from the tank/cell, if not you should. Pressure is better maintained with more volume.

 

[Cudafever]

Agree but i update from the standard 5/16 to 3/8 line and then a return back to the tank when i put this pump in.
This isn't some high HP eng. it makes maybe 450 HP

 

[yellow rose]

Yup at 6 psi first gal 55 sec 2nt gal 52 sec later 3d gal, another 55 sec later and the final gal took 51 sec.
Average =52.75 Seconds per gal

Yes i would have to raise the psi on the regulator to get a apples to apples comparison between 6 and 9 psi flow.

This is the pump i'm running.
Walbro High-Pressure Inline Fuel Pumps GSL392BX

Why are you running that pump? I don't know of any carb type regulator that is set up to regulate from 87 pounds down to 7 or so. Not even close. The very most I ever ran was 35 and it took a return line to make that work, long before anyone was using a return line.

 

[PRH]

I know Aeromotive has a two stage regulator to go from EFI type pressures down to carb pressures.

 

[yellow rose]

Know Areomotive has a two stage regulator to go from EFI type pressures down to carb pressures.

That's good to know. Never seen it but I'm sure it's needed to bring the carb pressure into line from that line pressure.

 

[PRH]

EFI to Carb Dual Stage Fuel Pressure Regulator – Aeromotive, Inc

I guess for me to fuel system as a whole is still a bit of a question mark.
For the easy test, I’d get a cheap gauge and plumb it up with some rubber line and tape it to the windshield and see what it reads when the motor is laying down in high gear.
“In theory”, if the system is 100% capable....... the gauge should read the same at that point as it does at idle.
If it won’t hold 9psi(the current setting), then I’d drop the setting to whatever the gauge read at the top of high gear, and see if the pump will maintain whatever that pressure is.

If there is currently a single regulator in the system, and as it sits the pressure doesn’t hold steady at wot for the entire pass....... I’d probably piggy back a couple of regulators.........since the dual stage thing is pretty pricey.
I’d have the first stage go from the 87psi pump pressure down to about 20-25psi, then the second stage from that 20-25 down to 6-ish.

My friends Stocker runs a magna-fuel 500 pump, #10 line from the pump to the reg, #8 to the carb......... gauge never moves from wherever you set it.
I think his pump would maintain 6.5psi if it was 1/2 worn out.

 

[Cudafever]

All i can tell yeah is i have been using this pump for over 3 years with no problem. with a mallory 4 port regulator.
I'm just going to have to find a fuel cap for a a#6 AN fitting so i can settle this once and for all.
This is my only day off so it may take a bit but this final test will be proven One Way or Another!

 

[Cudafever]

That's good to know. Never seen it but I'm sure it's needed to bring the carb pressure into line from that line pressure.

Just because the pump can produce 70= psi don't mean the return line is not big enough to hold it at 9 psi.
I have a gauge on the regulator and it hold 9 psi.

 

[PRH]

Is that Mallory regulator designed to go from 87psi to 9psi in one stage?

Have you ever put a gauge on the inlet side of the regulator to see what the operating pressure is on that side of the system?
As the demand is increased, does the inlet pressure drop as well?
If it does, does that impact the effectiveness of the regulator to maintain the outlet pressure?
I think this is where the idea of the dual stage regulator has merit.

My primary concern isn’t that the pump can’t supply enough fuel.
It can....... it was about 50 seconds for a gallon@6psi.

But....... it won’t at the pressure setting you’re using(9psi).
If the pump will only maintain 6psi at WOT, but the floats were set with the pressure at 9psi....... then the floats drop as the car moves down the track as the pressure is falling.

You’d be surprised how much a float has to drop to uncover enough area in the N/S to keep up with the high demand at full power/wot.
When you lower the pressure....... the float has to drop even further to make the area at the N/S even bigger.

The lower the float, the lower the fuel level, the leaner the mixture.

You tell me...... what’s making your motor lay down, 1/2 way through high gear....... after it’s already pulled cleanly through 2 gears.

 

[Cudafever]

Probably not.
EFI to Carb Dual Stage Fuel Pressure Regulator – Aeromotive, Inc

That's a one "big price tag" to control pump pressure to 16 and carb pressure to 9
The first stage will get it down to 9 psi. just like mine............. Just saying.

• Controls pump/line pressure from 8-16 PSI.
• Controls carburetor pressure from 5-9 PSI.

 

[PRH]

im not going to argue anymore.

But here is what we do know from the tests you did.
The current system, as you have it set up....... doesn’t have enough capacity to maintain 9psi at wot....... unless your motor is only making about 350hp.
Is maintained enough flow at 8psi to support about 375hp.
If you’re making 450-500hp, the system pressure(and float level) will be even lower.

So if you set the floats at 9psi, then after your foot hits the floor and the rpm starts to climb, the pressure at the N/S drops...... and so do the floats.

One more test to try if you feel like it.

Set the regulator to 6.5psi, set the ball valve for 5.5 and 6.0psi(test both), and see if it’s still in the 50 second range per gallon.

If it is....... leave the regulator set like that.

 

[Cudafever]

yes i don't what to either.
I will do the test and we will go from there.............it may take several day before i can get the cap and do the testeing.

So yesterday i went out and warmed up my car set my fuel levels at exactly center of the sight glass, got it good and warm and tested throttle response in neutral and in gear, not stumble
took it out on the road and no stumble at all.........Yup middle of 3 gear she starts poping and banging.
I know that if i raise my secondary bowl up to 3/4 site glass it will bog and not pop again.

Frustrating, but something has been digging at me and i need you guys opinion.
May be grasping at straws...but.....

So you know that little spring behind them center hung floats.
My front float spring really don't do much except just before it hits the bottom of the bowl. On the secondary side it has tension on it all the time. Not so much as to hold the float off the floor or any thing like that but. but if you lay the fuel bowl on its back, so you can see straight down into the bowl. the spring will close the needle. on the front it won't.

Which set up is wrong..........OR does it even matter. like i said the weight of the float will overcome the spring and set in the bottom of the float bowl. there is just a lot more tension on the back bowl spring.

so nobody responded about the float spring......No big deal??

 

[Mattax]

so nobody responded about the float spring......No big deal??

I thought it was a little odd especially if it affects the dry setting. see post 439.
To add to that. IMO the fuel level should be the controlling factor.
With big window bowls, middle is is the baseline and it seems like the bottom is about as low as one would ever adjust it.
Question is why does it need to be that low?
Maybe my brain is still foggy in the morning. But when especially when setting wet, a stronger spring or weaker spring should not affect the end result.

Not many inlet systems can hold steady much above 6 or 7 psi.
The larger the valve, the more difficult it is.
Lets say the needle was a circular face.
.110" diameter = .0095 sq. in of surface area;
multiply by 9 lbs/sq in => .089 pounds force trying to push the valve open.
multiply by 7 lbs/sq in => .067 pounds force trying to push the valve open.
multiply by 4 lbs/sq in => .038 pounds force trying to push the valve open.
.130" diameter = .0133 sq. in of surface area;
multiply by 9 lbs/sq in => .119 pounds force trying to push the valve open.
multiply by 7 lbs/sq in => .093 pounds force trying to push the valve open.
multiply by 4 lbs/sq in => .053 pounds force trying to push the valve open.

Knowing that Holley considered 7 psi about the limit its floats and valves could control, and that 110 were about as big as typically offered for gasoline, .067 pounds is probably about the limit of what a float can push back against and really hold it shut.
(A longer arm will give it more leverage, and there are some different lengths available for when that's needed.)

Maybe it is holding steady at 9 psi while parked, but when the fuel is sloshing around a little that could be enough to cause the valve to crack open when the fuel level hasn't really dropped.

Just maybe that is the answer to the question:
With 9 psi in the feed lines, setting the fuel level in the bowls low at idle got closer to correct level under different conditions.
???
To take it further, the delivery issues you guys were discussing last night might result in inadequate refill down the track at WOT.
???

 

[Cudafever]

The fuel delivery, i'm just not going to comment on until i have data.
I have allway ran 9 psi on a holley. a Carter carb won't handle it. Even my mechanical pump ran 8.
like your numbers above!

Just to clear up the site glass........both the front and back bowls were set above center. front was just slight off and the back was about 3/4 of the sight glass. When i lowered them both and reset the fuel mixture screws is when i got rid of the stumble and got the lean pop back.

 

[Cudafever]

In my holley book it said that the stiffer float spring would cause a lower float level and a weaker one would cause a higher float level............My take on it is it don't matter because you will set the float at the right level, with either spring tension??????

 

[PRH]

Here’s my current thinking.......

The reason you had no flow with the ball valve set for 9psi is....... it was(most likely) closed.
If you cracked it open at all, I can’t understand how there would be no flow.
The “concern” I have is, the flow went from 50 seconds at 6psi to 115 seconds at 8psi.

Pressure flows from high to low, so I understand there’s going to need to be some pressure differential at the ball valve to get flow.

The test with the lower pressure is just to see if the system will provide adequate flow and maintain system pressure with something less than a 2psi pressure drop.

Before doing the test with the regulator set for 6.5......
While it’s still set at 9psi, I’d try adjusting the ball valve up from 6psi a 1/2lb at a time, just to see about how much pressure the system, as currently set, will maintain while pumping a gallon in about 85 seconds.
We know 6psi is in the low 50’s, 8psi is almost 2mins....... is 7psi close to 85 seconds?

The reason I’m focused on this is, I’ve never seen the symptoms your experiencing have anything to do with the carb calibration.
If it was carb/fuel related......it was a supply problem........ in as much as the bowls weren’t staying full enough.

The odd thing about it is....... it didn’t seem to do this when those bowls were on the Demon body, right?

 

[joec]

Isnt the trick to use lower pressure with enough flow. If at 5 or 6 lbs there is enough flow use it .At 7or more lbs isnt it aerating the fuel in the bowl more??

 

[Mattax]

I think he is focusing on what what the pumps can supply and how they interact with the regulator.

I prob shouldn't answer for Dwayne though.

I wonder if Mallory has some flow graphs at different pressures. I do have a little bit of Mallory tech liturature from 15-20 years ago. If the pump you have was also made back then, I can take a look.

Just to look at how presure and flow relate with a typical electric pump, here's a couple graphs from the 2014 Holley catalog.

 

[PRH]

In terms of absolute capacity, CF’s fuel system has plenty of flow.
It’s way better than 85 seconds at 6psi....... so, fundamentally it’s fine.
At this point I’m just seeing if there is a way to adjust the regulator differently so there isn’t a 2psi system pressure drop when going from idle (9psi) to wot at rpm (7-ish psi)........ to try and minimize the float drop.

If none of that seems to have any impact on the laying down in high gear...... then the “what I would do” test would then be put the Demon completely back together, put it back on and verify that with the same bowls, and the floats adjusted the same way...... it doesn’t lay down 1/2 way thru high gear(after pulling strong through the first two gears).

 

[Cudafever]

Here’s my current thinking.......

The reason you had no flow with the ball valve set for 9psi is....... it was(most likely) closed.
If you cracked it open at all, I can’t understand how there would be no flow.
The “concern” I have is, the flow went from 50 seconds at 6psi to 115 seconds at 8psi.

Pressure flows from high to low, so I understand there’s going to need to be some pressure differential at the ball valve to get flow.

The test with the lower pressure is just to see if the system will provide adequate flow and maintain system pressure with something less than a 2psi pressure drop.

Before doing the test with the regulator set for 6.5......
While it’s still set at 9psi, I’d try adjusting the ball valve up from 6psi a 1/2lb at a time, just to see about how much pressure the system, as currently set, will maintain while pumping a gallon in about 85 seconds.
We know 6psi is in the low 50’s, 8psi is almost 2mins....... is 7psi close to 85 seconds?

The reason I’m focused on this is, I’ve never seen the symptoms your experiencing have anything to do with the carb calibration.
If it was carb/fuel related......it was a supply problem........ in as much as the bowls weren’t staying full enough.

The odd thing about it is....... it didn’t seem to do this when those bowls were on the Demon body, right?

I can do that, maybe tomorrow if i get off work at a decent time.

 

[Cudafever]

Isnt the trick to use lower pressure with enough flow. If at 5 or 6 lbs there is enough flow use it. At 7 or more lbs isn't it aerating the fuel in the bowl more??

This i have never considered